The goals of this project are to characterize lymphocyte Fcy receptors genetically and functionally. Recent findings indicate that the Fcy receptors of B lymphocytes interact with: a) the lymphocyte cytoskeleton, b) Ia antigen;s and Lym antigens, c) surface IgM, and d) surface IgD. Each of these interactions is distinct, specific, and non-random. In additional, monoclonal antibodies specific for FcyR induce B lymphocytes to both proliferate and secrete antibody (function). This response does not require T lymphocytes and is specific by a variety of criteria. This is the only antibody specific for a B lymphoctye receptor which triggers function. These findings strongly suggest that B lymphocyte Fcy receptors are central to B lymphocyte activation and immunoregulation.